It is a common practice to use precast concrete modules to build concrete structures rather than erect a form on the site to pour the entire structure in position. The modules can be precast in standard shapes and sizes, with reinforcing rods and various inserts, and delivered to the site to be assembled into the structure. For example, rectangular concrete culverts are easy constructed by precasting concrete C-channels in standard modular lengths, joining module pairs, one on top of the other, at their respective wall sills to produce a rectangular culvert section, and joining such sections end-to-end to the desired overall length.
In addition to channel modules, other modular shapes such as rectangular boxes, squares, and pentagons are use to form more complex structures such as sub-terrain tanks, vaults and habitable enclosures.
The modules are cast in reusable forms. A representative form of this type is described in U.S. Pat. No. 3,539,146. For brevity, the disclosure of that patent is incorporated herein by reference so that details concerning operation of the form need not be repeated here in great detail.
In simplest terms, such forms can be described as comprising a base with inner and outer form sections attached thereto, with a base plate located between the inner and outer form sections. As shown in the referenced disclosure of U.S. Pat. No. 3,539,146, the base plate may be configured to mold a mating keyway into the wall sills, such as the tongue and groove keyway disclosed in its drawings. This requires using different base plates for the opposing concrete sections, such as the tongue producing plate 34 shown in FIG. 3 of U.S. Pat. No. 3,539,146 and the groove producing plate 34 shown in its FIG. 5.
It is also known to use inside and outside rabbets (also called "rebates" or "ship laps") as keying structure to join concrete sections. This inventor believes the mating rabbets to be a superior keying structure for joinder of massive concrete structures, such as the culvert section (10) depicted in FIG. 1 herein. A concrete module (12), formed with an inside rabbet on its wall sills, is placed in the culvert excavation as the bottom of the culvert. Then a module (14), formed with an outside rabbet on its wall sills, can be lowered onto it, letting the walls of the rabbets contact and center the upper module in place as it is lowered. The seam can be tarred or caulked if necessary for water tight integrity.
In the prior art of casting concrete, rabbets have long been made by inserting a rectilinear bar or an L-angle bar into the form at the wall sill, such as disclosed in U.S. Pat. No. 939,059 (see inserts 17 and rabbet 151 therein). However, for joinder of massive concrete structures, such as the culvert section (10) depicted in FIG. 1 herein, this inventor believes that the mating rabbets should have sloped upright walls with rounded shoulders, rather than sharp vertical walls that would be formed by right angle inserts. This shape allows the top module to be lowered onto the bottom module and be centered by the rabbets more easily.
An objective of this invention is to provide a mold insert that can be inserted in a concrete form apparatus to produce such sloped rabbets, and in particular to be capable of producing both inside and outside rabbets. This objective would be achieved by a mold insert which in one orientation produces an outside edge rabbet in the concrete, and when inserted in an inverted orientation produces an inside edge rabbet in the concrete.
A further objective is to provide a mold insert with improved sealing and close conform fit between the inner and outer form sections to seal against seepage of liquid concrete mix past the insert.
A further objective is to provide a mold insert which can be expanded in width, elongated, and/or end-mitered as necessary to accommodate forms which produce a variety of module shapes.
A further objective is to produce a mold insert that can bear the weight of a large column of liquid concrete, yet be sufficiently light-weight that it can be easily removed from the forming apparatus.
The manner in which such objects are achieved by the present invention will be apparent upon reading the detailed description which follows, with reference to the drawings for illustration of a particular embodiment. By way of overview, and to assist cursory searchers who do not wish to read the entire disclosure, the following section is provided as a brief summary disclosure of the invention in perfunctory and informal terms. However, persons seeking to understand the full scope of the invention should be aware that such understanding can only come from careful reading of the claims found at the end of this document.